The present invention relates to a structure of an in-plane switching mode liquid crystal display (LCD), and more particularly to a structure of an in-plane switching mode TFTLCD with an improved aperture ratio of the pixel region thereof. The present invention further relates to a simplified process for forming an in-plane switching mode LCD.
With the development and improvement on LCD-related technology, a liquid crystal display tends to substitute for a conventional cathode-ray tube display to become a main stream. Please refer to FIG. 1A which is a schematic circuit diagram of a unit pixel region in a liquid crystal display. In the unit pixel region, a thin film transistor (TFT) 11 functioning as a switching unit, a displaying unit 12 and a storage capacitor 13 are included. Concerning the structure of the display unit 12, it can be classified currently into two types, i.e. a twisted nematic mode LCD (TN-LCD), and an in-plane switching mode LCD (IPS-LCD).
A general structure of the display unit 12 of a TN-LCD is schematically shown in FIG. 1B. The display unit 12 includes a data electrode 121 and a common electrode 122 which are spaced with a cell gap d, and liquid crystal (LC) molecules 123 sandwiched between the electrodes 121 and 122. By providing a potential difference between the data electrode 121 and common electrode 122, the LC molecules 123 will tend to stand, and the standing angles of the LC molecules relative to Z-axis depend on the electric field applied thereonto. For illustration, three kinds of electric fields E1, E2 and E3 are applied in FIG. 1B to show the changes of the standing angles of LC molecules wherein E1 greater than E2 greater than E3=0. For different standing angles, the light transmittance varies, thereby controlling the brightness of individual pixels. The rotation manner of the LC molecules in such a TN-LCD result in a change of light transmittance with different viewing angles. For example, the light transmittance in the A-Axe2x80x2 direction and that in the B-Bxe2x80x2 direction are different because their multiple refraction in different ways. Therefore, the viewing range of such an LCD, especially a large-size LCD, for seeing a clear image is confined.
A general structure of the display unit 12 of an IPS-LCD is schematically shown in FIG. 1C. As shown, the data electrode 121 and the common electrode 122 are arranged at the same side of LC molecules 123. Similar to the operations for a TN-LCD described above, a potential difference is provided between the data electrode 121 and common electrode 122 to rotate the LC molecules 123. According to the in-plane switching mode, the LC molecules 123 will rotate about the Z-axis to a degree depending on the electric field applied thereonto. For illustration, three kinds of electric fields E4, E5 and E6 are applied in FIG. 1C to show the changes of the rotating angles of LC molecules wherein E4 greater than E5 greater than E6=0. For different rotating angles, the light transmittance varies, thereby controlling the brightness of individual pixels. The rotation manner of the LC molecules in such an IPS-LCD will not result in any significant change of light transmittance with different viewing angles. Therefore, it has an advantage of providing a broad viewing range, and thus is suitable for large-size display.
A general in-plane switching mode TFTLCD is schematically shown in FIG. 2 which is a partial top plane view of the LCD structure. A conventional process for manufacturing the LCD structure principally includes the following steps:
(a) forming a first metal layer, and defining a gate conductive line 21 of TFT units and common electrodes 22 of display units;
(b) depositing a tri-layer structure which includes a gate isolation layer, a semiconductor layer, and an etch-stopper layer;
(c) defining an etch-stopper structure;
(d) forming a doped semiconductor layer, and defining source/drain regions of TFT units;
(e) forming a second metal layer, and defining a data line 23 of TFT units and data electrodes 24 of display units;
(f) depositing a passivation layer, and defining contact vias for interconnection; and
(g) forming a transparent conductive layer, and defining transparent electrodes.
In the above conventional process, the common electrodes 22 and the data electrodes 24 are formed of the first and second metal layers by different photo-masking and lithography procedures, respectively. As known, for each photo-masking and lithography step, the risks of misalignment (i.e. L1xe2x89xa0L2 in FIG. 2) and contamination may be involved so as to affect the production yield. Further, the opaque feature of metal results in the reduction of light transmittance, and thus a relatively large clearance between each pair of data and common electrodes is required in order not to influence the overall light transmittance of the pixel region too much. The relatively large clearance, however, results in a relatively high operational voltage.
In order to solve these problems, a transparent conductive material substitutes for metal to form the common and data electrodes so as to enhance the light transmittance or allow the clearance to be reduced to a level less than the cell gap d. For example, indium tin oxide (ITO) can be used therefor. Nevertheless, the common and data electrodes are still defined by different photo-masking and lithography procedures, so the possibility of misalignment still exists. If such misalignment is desirably made to be tolerable, the compactness of the device cannot be achieved. Furthermore, the conductivity of the transparent conductive material is not good enough for electric conduction, so additional metal layers are required for forming the scan line and the data line. Thus the manufacturing process is even complicated.
Therefore, an object of the present invention is to provide a process for forming an in-plane switching mode liquid crystal display (IPS-LCD), which simultaneously defines pixel portions of the common and data electrodes so as to avoid misalignment.
Another object of the present invention is to provide a process for forming an in-plane switching mode liquid crystal display (IPS-LCD), which simultaneously defines the data line and the transparent pixel portions of the common and data electrodes so as to be relatively simple in manufacturing.
A further object of the present invention is to provide an in-plane switching mode liquid crystal display (IPS-LCD), in which a storage capacitor consisting of storage-capacitor portions of the common and data electrode structures is disposed outside the pixel region so as to enhance the aperture ratio of the pixel region.
The present invention relates to a process for forming an in-plane switching mode liquid crystal display (IPS-LCD), comprising steps of providing a substrate made of an insulating material; forming a first conductive layer on a first side of the substrate, and defining a gate conductive structure, and a bus portion of a common electrode; forming a tri-layer structure consisting of a gate insulation layer, a semiconductor layer, and an etch stopper layer; defining an etch stopper structure with a portion of the semiconductor layer exposed; forming a highly doped semiconductor layer, and defining a contact via for interconnection to the bus portion of the common electrode; forming a second conductive layer, and defining source/drain regions, a data line, a pixel portion of a data electrode, and a pixel portion of the common electrode with the etch stopper structure and the gate insulation layer as a stopper, wherein the pixel portion of the common electrode is interconnected to the bus portion of the common electrode through the contact via; and forming a passivation layer, and defining a pixel region for exposing the pixel portions of the data and common electrodes.
Preferably, a storage-capacitor portion of the common electrode is simultaneously defined together with the gate conductive line and the bus portion of the common electrode, and/or a storage-capacitor portion of the data electrode is simultaneously defined together with the source/drain regions, the data line, the pixel portions of the data and common electrodes. More preferably, a storage capacitor consisting of the storage-capacitor portion of the data electrode and the storage-capacitor portion of the common electrode is disposed between a boundary of the pixel region and the gate conductive line.
In an embodiment, pixel portions of the common and the data electrode structures are both of a comb shape, and arranged opposite to each other with alternate comb teeth.
Preferably, the first conductive layer is formed of chromium, molybdenum, tantalum molybdenum, tungsten molybdenum, tantalum, aluminum, aluminum silicide, copper, or a combination thereof. The insulation layer is formed of silicon nitride (SiNx), silicon oxide (SiOx), silicon oxynitride (SiOxNy), tantalum oxide (TaOx), aluminum oxide (AlOx), or a combination thereof. The etch stopper layer is formed of silicon nitride (SiNx), silicon oxide (SiOx) or silicon oxynitride (SiOxNy). The semiconductor layer is formed of intrinsic amorphous silicon, micro-crystalline silicon or polysilicon. The doped semiconductor layer is formed of highly doped amorphous silicon, highly doped micro-crystalline silicon or highly doped polysilicon. The passivation layer is formed of silicon nitride or silicon oxynitride. The insulating substrate is a light-transmitting glass.
In an embodiment, the second conductive layer is formed of a transparent material selected from indium tin oxide, indium zinc oxide and indium lead oxide. Alternatively, the second conductive layer is a composite layer including a transparent electrode layer and a metal layer overlying the transparent electrode layer. Preferably, a portion of the metal layer in the pixel region is removed after the data electrode and the pixel portion of the common electrode are exposed. The metal layer can be formed of chromium, molybdenum, tantalum molybdenum, tungsten molybdenum, tantalum, aluminum, aluminum silicide, copper, or a combination thereof. The transparent electrode layer can be formed of indium tin oxide, indium zinc oxide, or indium lead oxide.
Preferably, the step for defining the etch stopper structure includes sub-steps of forming a photoresist layer on the tri-layer structure; providing an exposing source from a second side of the substrate opposite to the first side by using a remaining portion of the first conductive layer as a shield to obtain an exposed area and an unexposed area; and removing the photoresist and the etch stopper layer of the exposed area so that the remaining portion of the etch stopper layer in the unexposed area has a specific shape substantially identical to the shape of the remaining portion of the first conductive layer, thereby exposing a portion of the semiconductor layer of the exposed area.
The present invention also relates to an in-plane switching mode liquid crystal display (IPS-LCD), comprising a first insulating substrate; a second insulating substrate; liquid crystal molecules sandwiched between the first and second insulating substrates; a thin film transistor (TFT) structure disposed on the first insulating substrate; a common electrode structure disposed at the first insulating substrate, and including a pixel portion and a storage-capacitor portion; a data electrode structure disposed on the first insulating substrate, electrically connected to a source electrode portion of the TFT structure, and including a pixel portion and a storage-capacitor portion; and a passivation structure overlying the TFT, common electrode and data electrode structures with a pixel aperture exposing the pixel portions of the common and data electrode structures; wherein a storage capacitor consisting of the storage-capacitor portions of the common and data electrode structures is disposed between a boundary of the pixel aperture and a gate conductive line of the TFT structure.
Preferably, the common electrode structure further includes a bus portion.
Preferably, the pixel portions of the common and data electrode structures are formed with the same transparent electrode layer formed of indium tin oxide, indium zinc oxide, or indium lead oxide.
Preferably, the pixel portions of the common and data electrode structures are formed with the same composite layer consisting of a transparent electrode layer and a metal layer. The metal layer can be formed of chromium, molybdenum, tantalum molybdenum, tungsten molybdenum, tantalum, aluminum, aluminum silicide, copper or a combination thereof. The transparent electrode layer can be formed of indium tin oxide, indium zinc oxide or indium lead oxide.
Preferably, the passivation structure is formed of silicon nitride and silicon oxynitride. The first and second insulating substrates are formed of light-transmitting glass.
Preferably, the pixel portions of the common and the data electrode structures are both of a comb shape, and arranged opposite to each other with alternate comb teeth.